The lens of the human eye frequently develops cataracts with age. Cataracts are often corrected by surgically removing the natural lens and implanting an artificial intraocular lens (IOL). Appropriate IOL power can vary by as much as 20 diopters from person to person, and selecting the correct IOL power is a significant challenge. In fact, IOL power is incorrectly selected in up to one-third of cataract surgeries. These patients will unfortunately require additional corrective lenses for some or all activities.
A major limitation in selecting the appropriate IOL power is the current inability to accurately predict Effective Lens Position (ELP), the distance from the IOL to the apex of the cornea. The analogous preoperative distance is called the Anterior Chamber Depth or ACD, which is the distance from the natural lens to the apex of the cornea. ACD can be measured (see, e.g., U.S. Pat. No. 6,631,990), but for several reasons, ACD is not equal to ELP. First, the natural lens is several times thicker than an IOL, and the natural lens varies in thickness from patient to patient. The thickness of the natural lens presses outwardly on the iris such that the pupil is nearer to the cornea. Also, the natural lens is contained within a capsular bag located against the vitreous body behind it, but postoperatively, the IOL may be suspended within the capsular bag, without resting against any surface along the axial axis.
There is a need for devices and methods that can measure axial distances intraoperatively. There is a particular need for devices and methods to more accurately predict Effective Lens Position and thus, more accurately select IOL power to improve cataract surgery outcomes.